1999 AUDI A4 fuel

24-55
If specified value is not obtained:

- Replace central electronics.

Checking activation of Fuel Pump (FP) relay

- Switch ignition off.

- Connect VAG1598/31 test box at wiring harness
to Engine Control Module (ECM), do not connect
ECM Page 24
-19
.

- Switch ignition on.

- Bridge terminals 1 and 65 at test box using wires
from VAG1594A adapter test kit.

If relay triggers now, but didn't during output DTM:
If relay does not trigger:
Fuel Pump (FP) relay (at position 4 of central electronics in driver's
footwell, left) must trigger.
- Replace Engine Control Module (ECM) Page 24
-22
- Switch ignition off.
- Remove cable bridge.
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- Remove Fuel Pump (FP) relay.
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24-57

- Repair open circuit or short circuit if
necessary.
If no malfunctions are detected:

- Replace Fuel Pump (FP) relay -J17-.

- Re-connect Engine Control Module (ECM).

Check voltage supply for Fuel Pump (FP) and
components

- Remove fuses S228, S232, and S234 (positions 28, 32, and 34) from
fuse holder.
- Initiate output Diagnostic Test Mode (DTM) Page 01
-51
and activate
Evaporative Emission (EVAP) canister purge regulator valve -N80-.
- Connect multimeter for voltage measurement to Ground (GND) and to
one terminal of the following fuses in the fuse holder. Circlip
Specified value at one of the terminals
S228 approx. battery voltage
S232 approx. battery voltage
S234 approx. battery voltage
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24-58
If specified values are not obtained:

- Repeat test at another terminal of fuse socket.
If specified values are not obtained again:

- Check wire connections.

Electrical Wiring Diagrams, Troubleshooting &
Component Locations If no malfunctions are detected:

- Replace Fuel Pump (FP) relay -J17-.

- Re-insert the fuses.
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24-63
Evaluation display group 002 Display field:
3
Possible cause
Corrective action
less than 1.0
ms
Smaller values are only possible when driving in
deceleration mode
larger than
4.0 ms Engine under load due to power accessories.- Reduce load (A/C system/power
steering/generator)

Poor idle (does not run on all cylinders)- Check spark plugs.
- Check fuel injectors Page 24
-37
.


Throttle valve control module - J338- faulty- Check throttle valve control module
Page 24
-124

Display field:
4
Possible cause
Corrective action
smaller than
2.0 g/s
large false air mass between intake manifold and Mass Air
Flow (MAF) sensor
Voltage supply of Mass Air Flow (MAF) sensor or wire
connections to Engine Control Module (ECM) - Check intake system for leaks (false air)
Page 24
-68
.
- Check voltage supply and wire
connections Page 24
-64

larger than
4.5 g/s
Engine under load due to power accessories.- Reduce load (A/C system/power
steering/generator)

Voltage supply of Mass Air Flow (MAF) sensor or wire
connections to Engine Control Module (ECM) - Check voltage supply and wire
connections Page 24
-64

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24-64

Voltage supply for Mass Air Flow (MAF)
sensor, checking

Test requirements:

Fuse for Mass Air Flow (MAF) sensor OK

Electrical Wiring Diagrams, Troubleshooting &
Component Locations

Fuel Pump (FP) relay OK; checking Page 24
-52
.

Note:
Voltage is supplied to Mass Air Flow (MAF)
sensor from Fuel Pump (FP) relay.

- Disconnect connector from Mass Air Flow (MAF)
sensor.

- Connect multimeter for voltage measurement as follows.Harness connector
Terminal
Measure to
2 Engine Ground (GND)
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24-65
If specified value is not obtained:

- Check wire connection from terminal 2 of
connector to Fuel Pump (FP) relay via fuse for
open circuit and short circuit to Ground (GND):

Electrical Wiring Diagrams, Troubleshooting &
Component Locations
- Repair open circuit or short circuit if
necessary.

Note:
Ground (GND) from the ECM is present at terminal 3 of connector.
If specified value is not obtained: - Connect multimeter to terminal 2 and terminal 3 of connector for
voltage measurement.
- Operate starter briefly (engine can also start).

Specification: approx. battery voltage
- Check wire connections Page 24
-67
.
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24-68

Intake system, checking for leaks
(unmetered air)


Special tools and equipment

Notes:
Test sequence
VAS5051 with VAG5051/1Engine leak detection spray G 001 800 A1The negative pressure in the intake system sucks in the leak detection
spray with the unmetered air. Leak detection spray decreases ignition
quality and performance of the fuel mixture. This causes a reduction in
engine speed and a sharp increase of CO content. It is absolutely necessary to follow the safety precautions listed on the
can.
- Connect VAS5051 tester Page 01
-7 and select vehicle system "01 -
Engine electronics". Engine must run at idle for this.
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